The long-term objective of this proposal is to determine if receptors for fibroblast growth factors (FGF) can be used to develop therapeutic tools to prevent, or treat restenosis. The success of balloon coronary angioplasty remains compromised by a restenosis rate of 30-50%. Histologic studies indicate the neointimal thickening is largely due to the proliferation of smooth muscle cells (SMC). Studies in vitro have identified multiple mitogens for SMC, many of which are up-regulated after balloon injury, and no clinical therapies -- alone or in combination, including anti-coagulants, anti-platelet agents, calcium antagonists, lipid-lowering agents, or ACE inhibitors -- have markedly reduced restenosis rates. An alternative is to selectively ablate the proliferating subpopulation of SMC's using the recent observation that when these cells are proliferating they express more basic EGF receptors (FGFRs). When exposed to a conjugate of betaFGF and the ribosome- inactivating enzyme, saporin (SAP; which by itself enters mammalian cells very inefficiently), the proliferating smooth muscle cells (SMCs) are killed while the non-proliferating SMCs are spared because they have few FGFR. Endothelial cells, which have fewer FGFRs than SMCs, are killed only at higher doses and in fact are stimulated by doses that kill SMCs. This raises the possibility of using betaFGF, or an antibody to a FGFR, as a targeting vector for a single-dose, intravenous, cytocidal therapy. Simply put, the presence of multiple growth factors and their receptors make it difficult to inhibit SMCs with an antibody or other antagonist directed at betaFGF or any other growth factor or receptor. However, virtually all SMCs have FGFRs and so are killed by FGF-SAP; in other words, the cells are not protected by the presence of other growth factors. Because of the surprising finding that most of the seven FGF ligands bind most of the FGFRs, cell-specific targeting is likely to depend on which of the 6 FGFR genes (and which of their many alternatively-spliced forms) are up-regulated after vascular injury. The present proposal is 1) to determine if our recently expressed recombinant FGF-SAP can be used as a local or systemic therapy to prevent or reverse SMC accumulation in the balloon-injured rat carotid artery; 2) to evaluate the effect of FGF-SAP on ECs; 3) to screen for major toxicity; 4) to determine which FGFRs are up-regulated in injured vessels by analysis of PCR extension products of FGFR primers, using mRNA from ballooned rat carotid arteries and human coronary atherectomy specimens; 5) to determine the cell source of the receptor mRNAs by simultaneous in situ hybridization and cell type- specific immunocytochemistry; 6) determine whether there is a FGFR isoform specific for proliferating SMCs; 7) develop monoclonal antibodies to an extracellular domain of that isoform (for eventual use in diagnostic imaging and therapeutic targeting).